1. Field of The Invention
The present invention relates to a structure of liquefied hydrogen pump suitable for use in discharging and supplying, for example, hydrogen liquefied under an extremely low temperature in a fuel tank to a hydrogen (ignited) engine.
2. Description of The Background Art
A previously proposed structure of a liquefied hydrogen pump used in a fuel supply apparatus for a hydrogen ignited engine will be explained below.
A hydrogen fuel tank is installed to reserve the liquefied hydrogen. The hydrogen fuel tank is formed with a so-called double wall structure made of heat insulating materials (adiabatic materials). A vacuum layer is formed between the two heat insulating walls. In addition, the liquefied hydrogen having a volume of approximately 100 liters is contained under a pressure of a range from approximately 0.05 MPa (Mega Pascal) to approximately 0.1 MPa.
In the fuel supply apparatus described above, a liquefied hydrogen pump is formed in a cylindrical shape with a bottom. The previously proposed liquefied hydrogen pump generally includes: an elongated pump housing vertically extended from an upper end toward a lower end; a cylinder fixedly secured around an inner periphery of the lower end of the pump housing; a piston slidably inserted and fitted into the cylinder, the piston reciprocating upward and downward within the cylinder; and a pump head projected externally from the tank.
The pump head includes a crankshaft rotatably driven via a belt wheel by means of an external DC motor; a cross head which reciprocates upward and downward within the pump head, the cross head being linked to the crankshaft via a connecting rod; and another connecting rod, located at a lower end of the cross head, formed in an elongated rod shape having a small diameter, and which reciprocates the piston in synchronization with the cross head within the cylinder.
A suction tube is, furthermore, provided at the bottom portion of the pump housing so as to communicate with the hydrogen fuel tank via a suction valve.
A discharge tube is disposed such that one end thereof is communicated with a discharge valve provided within the piston and the other end thereof is extended externally from the pump head. The discharge tube is vertically extended.
When the piston within the cylinder is reciprocated in the hydrogen fuel pump, the liquefied hydrogen within the hydrogen fuel tank is sucked from the suction tube via the suction valve so that the liquefied hydrogen is discharged externally from the suction tube under a pressure of, for example, approximately 10 MPa.
Next, a heat exchanger is interposed between a tip end of the discharge tube and engine body (to be described later). The heat exchanger is supplied with a hot water or so forth from an external equipment in order to heat the liquefied hydrogen discharged from the discharge tube so as to vaporize the liquefied hydrogen into hydrogen gas. The heat exchanger supplied the vaporized hydrogen gas by means of the hot water and so forth to a hydrogen injection valve via a supply tube located downstream of the heat exchanger.
A surge tank is provided in a midway through the supply tube. The surge tank contains the vaporized hydrogen gas at a normal temperature under a pressure of, for example, approximately 10 MPa so as to prevent pulsations in the hydrogen gas when the hydrogen gas is injected from the hydrogen injection valve.
The engine body is so-called hydrogen ignited engine. The hydrogen ignited engine generally includes: a piston which is reciprocated within a cylinder; and a cylinder head disposed above the cylinder so as to define a combustion chamber between the piston and cylinder. The cylinder head is provided with an ignition plug projected into the combustion chamber. The ignition plug ignites the hydrogen gas injected from the hydrogen injection valve within the combustion chamber so that a combustion pressure of the hydrogen gas is generated within the cylinder.
The hydrogen engine includes the hydrogen injection valve described above. The hydrogen injection valve is disposed in the cylinder head. The hydrogen injection valve includes a plunger which serves to open a valve body against a spring force of a valve spring so that the hydrogen gas from the supply tube is injected into the combustion chamber. It is noted that the plunger of the hydrogen injection valve is driven in its open direction under the instantaneous pressure when a high pressurized oil (hydraulic) is supplied via a distribution tube, for example, by means of, a fuel injection pump for a Diesel engine. Then, when the high pressurized oil is exhausted into a reservoir via a distribution tube, the valve spring serves to push the valve body toward its close direction.
When the crankshaft of the liquefied hydrogen pump is rotated via the belt wheel, the cross head is reciprocated within the pump head so that the piston linked to the cross head via the elongated connecting rod is reciprocated within the cylinder. The liquid hydrogen within the hydrogen fuel tank is sucked into the cylinder from the suction tube and discharged via the discharge tube. Then, the liquefied hydrogen discharged within the discharge tube is vaporized into the hydrogen gas by means of the heat exchanger. The vaporized hydrogen gas is supplied from the supply tube to the hydrogen injection valve via the surge tank.
In the hydrogen injection valve, the high pressurized oil from the injection pump causes the plunger to be driven so that the valve body is open against the spring force of the valve spring. During the open state of the valve body, the hydrogen gas having a pressure of approximately 10 MPa is injected into the combustion chamber of the hydrogen ignited engine. Then, the hydrogen ignited engine mixes the injected hydrogen gas with a suction air and ignites and burns the air-hydrogen mixture so that the generated combustion pressure causes the piston to be driven, thus generating a revolution output from its crankshaft.
Since, in the previously proposed fuel supply apparatus described above, the liquefied hydrogen is contained at the extremely low temperature of approximately -253.degree. C. under a pressure ranging from approximately 0.05 MPa to approximately 0.1 MPa and the liquefied hydrogen is discharged by means of the liquefied hydrogen pump into the discharge tube under the pressure of approximately 10 MPa, it is necessary to form (elongate) the connecting rod linking the piston and cross head in an elongated rod.
However, a large compressive weight is acted upon the elongated connecting rod described above when the liquefied hydrogen under a low pressure is pressurized up to, for example, approximately 10 MPa by means of the piston of the liquefied hydrogen pump. Consequently, such a trouble as a seating and flexing of the elongated rod would be easy to occur.
In addition, it is difficult for the piston linked to the cross head via the elongated connecting rod to be coaxially disposed within the cylinder. If the piston within the cylinder were slightly inclined with respect to the cylinder, a frictional heat would occur between the piston and cylinder during the slide motion of the piston. In worst case, the frictional heat causes the liquefied hydrogen to become easy to be vaporized so that it becomes difficult to maintain the internal of the hydrogen tank at the extremely low temperature.